The invention relates to a filter arrangement inserted in the intake airflow of a heating or air-conditioning system of a motor vehicle, having two filters (preferably activated carbon filters) arranged offset and at a distance one behind the other in the direction of flow, and through each of which a partial volume of the air to be filtered flows.
A space-saving filter arrangement of this generic type, having a multiplicity of filters arranged offset one behind the other, is disclosed in German Offenlegungsschrift 3,632,524. The intention of this arrangement is to divide the intake airflow upstream of each filter into an air quantity flowing through the upstream filter and an air quantity flowing downstream around this filter, so that only filtered air should be present downstream of the last filter. However, this filter arrangement, with air quantities which vary greatly in practical operation, cannot fulfill these expectations, since it is impossible to prevent portions of the air quantity from being filtered several times unnecessarily, while there is no guarantee that all portions of the air quantity have in the final analysis flowed through a filter. This is all the more true since the filter resistance increases as the operating time increases, and the air leaves the arrangement largely unfiltered because of the possibility of bypassing the filters.
The object of the present invention is to provide a filter arrangement of the generic type described above which supplies air to the two filters uniformly, even in the case of unfavorable and changing flow conditions, and at the same time ensures that only treated air is present downstream of the filters.
This object is achieved in a filter arrangement according to the invention, wherein an air-guiding device, which feeds air proportionately to the two filters, is arranged upstream thereof. Further, to increase the service life of the filters and in the case of a temporarily high air requirement, it is possible to create a bypass permitting air to flow around the filters, by swivelling a wall which is disposed in air flow path, or by swivelling a flap arranged on the wall.
In a preferred illustrative embodiment of the invention, the air-guiding device is designed as a guide blade arranged in the transition zone between the front side and the left-hand boundary of the filter situated at the front in the direction of flow.
Even very different approach flow conditions, for example caused by greatly changing air quantities, can be compensated if the guide blade is swivellable. For the purpose of setting the guide blade automatically, the pressure drop in the two filters can be detected and the guide blade adjusted until at least approximately equal pressure drop values prevail.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.